[add_dune_system_test] Dynamic and static variants should be connected when using the same =()=-type operator
The following example currently produces 6 executables and for each of those 3 inifiles.
[Grid]
File =2= ./grids/test_1p_1d.dgf, ./grids/test_1p_2d.dgf, ./grids/test_1p_3d.dgf
[__STATIC.COMPILE_DEFINITIONS]
GRIDTYPE =1= YASP, UG
GRIDDIM =2= 1, 2, 3
The desired output would be 6 executables where each has a single inifile. This is currently difficult as add_static_variants and add_system_test_per_target are called sequential in add_dune_system_test.